The Bay of Naples (population 3.7m) seen from the south-western slopes of the Vesuvius Volcano which last erupted in 1944. The national emergency plan to protect the inhabitants from a possible eruption of the Vesuvius area has as its baseline the explosive event of 1631. Drafted by the scientific community has identified three areas with different hazard defined: the red zone, yellow zone and the blue zone. The red zone is the area immediately surrounding the volcano, and is in greater danger as potentially subject to invasion by pyroclastic flows, or mixtures of gases and solids at high temperature which, sliding along the slopes of the volcano at high speed can destroy in a short time everything is on its way. Pyroclastic flows probably will not grow at 360 ° in the neighborhood of the volcano, but will head in one or more preferential directions